The present invention relates in general to textile machines, such as a machine for knitting narrow elastic, which utilize a knitted yarn package in the form of a continuous, unravellable strip and in particular to a new and novel apparatus for uniformly unravelling the knitted yarn package and for applying substantially uniform and constant tension to the unravelled yarn ends being fed to the machine.
Typically, textile machines for making narrow elastic fabric receive and knit together a plurality of elastic and conventional yarn ends from a number of individual yarn packages mounted on large creel frames adjacent to the machine. In order to reduce the floor space for the yarn supply arrangement and, in addition, to improve the efficiency and ease of transporting the yarn, it has become a common practice to knit a plurality of elastic yarn ends into a compact knitted yarn package which must be deknitted during the feeding operation. Examples of such yarn packages are illustrated in U.S. Pat. Nos. 3,827,261, 4,411,142 and 4,569,212. These methods of handling yarn have proven especially useful for elastic yarn, such as spandex, which may shrink, take a permanent set, or distort the yarn package during storage when handled conventionally, thereby presenting problems of nonuniform tension, snarling, and the like when the yarn is fed to the textile fabric making machine.
However, the use of knitted yarn packages of highly elastic yarns of relatively high denier has resulted in undesirably low feeding speeds which can cause significant economic losses over a period of time in view of the capital investment in a modern, high-speed, textile fabric forming machine since the unacceptable slow speed of deknitting such yarns does not permit the operator to take full advantage of the production capacity of the machine.
One prior art device for feeding and unravelling a knitted yarn package is illustrated in U.S. Pat. No. 3,542,084. A separate advancing mechanism passes the strip from the knitted yarn package through a pair of feed rolls. The motor driving the rolls is controlled by a relay activated by an electrically conductive finger which rests above the advancing yarn strip and a grounded bracket below the yarn strip. When the yarn unravels past the point where it is no longer between the finger and bracket, the relay is activated, thereby causing the motor to turn the feed rolls.
Certain disadvantages become apparent with such a design. First, if used with a yarn package having a plurality of ends, a single, incompletely unravelled yarn end could prevent the finger from contacting the bracket, thereby preventing the feed rolls from advancing the knitted yarn package. Second, no means are provided for controlling the tension as the strip is advanced. Third, no means are provided for adding tension over the amount necessary to cause the knitted yarn package to unravel. Finally, the design, as shown in FIG. 3 of the '084 patent, is not easily adaptable for feeding a modern textile fabric forming machine which is capable of using a plurality of knitted yarn packages and, consequently, would require a number of feeders for each textile machine.
Another well-known apparatus which has previously been adapted for feeding knitted yarn packages is illustrated in U.S. Pat. No. 2,920,772. This apparatus, commonly referred to as a "mousetrap", includes a plurality of parallel pins aligned perpendicular to the direction of movement of the knitted yarn package as it moves towards the textile fabric making machine. The pins are mounted alternately to an upper, pivoting member and a lower, stationary base member. The knitted yarn package is then passed between the plurality of pins. Tension is added by adding weight to the upper pivoting member to cause the pins mounted thereto to press against the moving knitted yarn package, thereby increasing the resistance to movement of the knitted yarn package.
Another device which is somewhat similar to the "mousetrap" is commonly referred to as a "ladder". This device also includes a plurality of parallel pins; however, unlike the "mousetrap", the pins are arranged similarly to rungs on a ladder. The knitted yarn package is then threaded over and under as many "rungs" as needed to provide sufficient tension to unravel the knitted yarn package.
Certain disadvantages are also apparent with both of these designs. First, no means are provided for ensuring uniform tension across the width of the knitted yarn package resulting in one or more yarn ends being under more or less tension than the other. Thus, the amount of these "latitudinal" tension variations may cause the fabric produced by, for example, a knitting machine, to skew since the amount of tension through one portion of the fabric may differ from the remainder of the fabric.
Second, no means are provided for controlling the tension in the direction of movement of the knitted yarn package after the tension initially has been set. Thus, minor changes in the textile fabric making machines's feed speed may result in differences in the amount of this "longitudinal" tension that may cause the pick count of the finished fabric to fall outside of prescribed limits. Furthermore, larger changes in the feed speed may result in "breakout" (i.e., the amount of tension exceeds the breaking strength of the yarn end) or "blow-up" (i.e., the amount of tension is less than the force needed to unravel the knitted yarn package and some incompletely unravelled yarn ends actually enter the textile fabric making machine).
It has thus become desirable to develop an apparatus for feeding a knitted yarn package having a plurality of yarn ends to a textile machine for knitting narrow elastic fabric that will uniformly unravel the knitted yarn package. In addition, it has become desirable to develop an apparatus for feeding a knitted yarn package that will apply substantially uniform and constant tension to the yarn ends being fed to the machine even if the speed of the machine changes. Finally, it has become desirable to develop such an apparatus which is simple to install, use, and maintain.